Universal Time (abbreviated UT) or Greenwich Mean Time (abbreviated GMT) is generally used when describing time globally. These terms are often used to refer to time kept on the Greenwich meridian (longitude zero). According to Greenwich meridian agreement, the earth is divided into 24 time segments, time zones, each of which takes 1/24 of the day. In the most common civil usage, UT refers to a time scale called “Universal Time Coordinated” (abbreviated UTC).
In connection to civil time, the Daylight Saving Time, DST, (or Summer Time as it is called in many countries) is introduced. DST is a way of getting more from summer days by advancing the clocks typically one hour during the summer. According to this, the sunset and sunrise are later than during normal time (i.e. winter time, standard time of the country in question). DST helps to save energy (less artificial light is needed during the evening) and to make the country more effective in addition to the pleasing effect of lighter evenings. The utilization of DST comprises adjusting the clocks typically one hour ahead when DST begins (during spring), and adjusting them back to standard time every autumn.
Approximately 70 countries utilize DST at least in a portion of the country. Japan is the only major industrialized country that has not adopted daylight saving. European nations have taken advantage of the time change for a long time and currently “summertime period” is standardized in the EU. EU's Daylight Saving Time runs from the last Sunday of March through the last Sunday in October.
For an example Moscow's standard time (UTC+3) is about a half-hour ahead of local mean time (UTC+2:30), which local mean time is the actual time in a given location based upon the Sun's position at the Midheaven (noon) of the place. This is about the same situation as in Detroit, where the standard time (UTC−5) is also about half-hour ahead of the local mean time (UTC−5:30). With their latitudes and with the relationship of their standard time to the local mean time the DST really helps to save daylight. In the Southern Hemisphere, where summer comes in December, DST is typically observed from October to March.
Equatorial and tropical countries (lower latitudes) do not observe DST since the daylight hours are similar during every season. This is why there is no advantage of moving clocks forward during the summer. China has had a single time zone since May 1, 1980 observing summer DST from 1986 through 1991, but currently they do not.
Most countries that observe daylight saving time are listed in the table below. Almost all of them save one hour in the summer and change their clocks some time between midnight and 3 am. Countries with “*” may have some specialities, which should be checked from national law.
ContinentCountryBeginning and ending daysAfricaEgyptStart: Last Friday in AprilEnd: Last Thursday in SeptemberNamibiaStart: First Sunday in SeptemberEnd: First Sunday in AprilAsiaMost states of theStart: Last Sunday in Marchformer USSR.End: Last Sunday in OctoberIraqStart: April 1End: October 1Israel(Estimate, Israel decides the datesevery year)Start: First Friday in AprilEnd: First Friday in SeptemberLebanon, KyrgyzstanStart: Last Sunday in MarchEnd: Last Sunday in OctoberMongoliaStopped in 2002Palestine(Estimate)Start: First Friday on or after 15AprilEnd: First Friday on or after 15OctoberSyriaStart: April 1End: October 1IranStart: the first day of FarvardinEnd: the first day of MehrAustraliaSouth-Australia,Start: Last Sunday in OctoberVictoria, AustralianEnd: Last Sunday in MarchCapital Territory,New South Wales,Lord Howe Island(saves half an hour)Australia—TasmaniaStart: First Sunday in OctoberEnd: Last Sunday in MarchFijiStopped in 2000New Zealand,Start: First Sunday in OctoberChatham*End: Third Sunday in MarchTongaStart: First Sunday in NovemberEnd: Last Sunday in JanuaryEuropeEuropean Union*,Start: Last Sunday in March at 1 amUK*UTCEnd: Last Sunday in October at 1 amUTCRussiaStart: Last Sunday in March at 2 amlocal timeEnd: Last Sunday in October at2 am local timeNorthUS*, Canada, MexicoStart: First Sunday in AprilAmericaSt. Johns, Bahamas,End: Last Sunday in OctoberTurks and CaicosCubaStart: April 1End: Last Sunday in OctoberGreenlandSame as EUSouthBrazilStart: First Sunday in NovemberAmerica(rules vary from yearEnd: Third Sunday in Februaryto year)equatorial Brazil doesnot observe DST.Chile*Start: Second Saturday of Octoberat midnightEnd: Second Saturday of March atmidnightFalklandsStart: First Sunday on or after 8SeptemberEnd: First Sunday on or after 6AprilParaguayStart: First Sunday in SeptemberEnd: First Sunday in AprilAntarcticaAntarctica(varies)
It can be clearly seen from the table above that there are many oddities in countries. For example some parts of the US and Canada do not observe DST, such as the state of Arizona (US) and the province of Saskatchewan (Canada). The observance can also be erratic. For example Chile delayed its changeover date for the Pope's visit in 1987 and a presidential inauguration in 1990.
In Japan, DST was introduced after World War II by the US occupation but was dispensed with in 1952 following opposition from farmers. Despite efforts by the Ministry of International Trade and Industry to have daylight saving introduced to cut Japan's energy consumption, opposition from farmers and the Ministry of Education maintains the situation.
Time zones will become important to people e.g. when travelling. Travellers need to know the time of the destination, according to which they are required to change the time from the country of departure (home country). Often the new time is informed to the traveller, whereby he/she can change the time of his/her watch. Similarly, when contacting another person abroad, the time of the country in question should be known for not disturbing the person e.g. during the night.
The time of electronic systems can be handled by means of a network. Personal computers or other fixed network devices need more information about the daylight saving time than about the time zone. However the use of portable electronic devices is constantly increasing as well as use of them in different countries. According to the characteristics of the devices, the devices can move from one location to another, which locations can also situate in different time zones. Currently movable devices utilize a mobile network, and by means of NITZ messages (Network Identity and Time Zone) received from the network, their time can be updated automatically. The NITZ informs the mobile device about a country code and the time zone, according to which the time in the mobile device can be updated.
The system time e.g. in Symbian based devices or Unix based devices runs in UTC. Due to this, the time is not changed by the change of the location or the start or the end of DST. The time presented to the user in the mobile terminal (referred as “home time”) takes into account the time zone and the possible DST. The events and marks in the mobile terminal are shown to the user in that time. In order to show the current home time correctly, the terminal's local information includes the universal time offset of the time zone and the information about the state of DST. When the user deals with future dates and times, the system does not know the state of the DST, and hence cannot deduce the correct UTC time for the home time given by the user. Also, when the user receives an event described in home time, the event is also stored as home time. Because the system cannot deduce the correct UTC time for the event, the event won't be in UTC time. The user may define which operations are implemented when the device moves from one time zone to another. The user may set on the automatic update of time and time zone (acquired by NITZ) whereby the time zone of the device is updated. The user may also update the time zone manually or the user may adjust the time of the device without adjusting the time zone. However, in all those cases the system will show the future events in the old home time, not in the new home time, and any alarms tied to these events will be launched at the wrong time.
A solution for solving the problem relating to time management of mobile phones is proposed by Sharp Laboratories of America. Their publication U.S. 2002/98857 A1 suggests a method wherein the clock of the mobile terminal synchronizes itself with a base station in any location, whereby the base station transmits a control signal including a UTC signal, a system identification signal, a network identification signal, a current local time signal and a DST flag. A selection mechanism is arranged into the clock by means of which the user can select a home time zone and to select a displayed time on the clock display from the group of displayed times consisting of current local time and home time zone. In addition the clock comprises a displayed time calculating mechanism that determines the time displayed on the clock display as a function of the current local time and home time zone.
The main defect in the related art is the one described earlier, a lack of a suitable method and a system according to which the updated time would reach the stored events, and update them as well. This kind of solution would be highly profitable, especially for those users who travel frequently and are tied to calendar and time.